I've an old Fiat dozer with a "under licence from Bosch" injector pump. Recently it was parked for a while (8 weeks) whilst I sorted out a clutch problem. Back in business but I now have a nasty surge. I checked the fuel pump oil and it had gone white so I figure water's got in there. I changed the oil but the problem obviously remains. The arrangement of the pump is a fuel control rod that moves back and forth under the control of a governor on the rear of the pump. For cold starts there's a button you depress that lets the fuel control rod go further forward for an extra shot of fuel. Depressing the button now has no effect, the rod doesn't click forward without some help (a finger through the inspection plug. ) and when the engine starts, it revs up, then often shuts down again. Same if the load varies suddenly, the pumps lagging. It's fine with a constant load that's brought on steadily, it's pushing well. It seems likely to me that the fuel control rod is sticking and the governor is struggling to shift it. What I'm chasing are suggestions for dealing with this, apart from pulling the whole pump down. I'm not clear in my mind exactly what the rod does, as I've never had to go into a pump that deeply. I know it moves the rack that controls the fuel delivery, but exactly how it does it and where it's likely to be sticky is the question.
In the absence of any replies I got stuck into this problem this afternoon. Pulled the side cover, the governor cover, and the end of the rack cover, off the pump and had a poke around. The rack was definitely sticking so I wriggled it back and forth, squirted penetrant at everything I could see and it freed up considerably. Re-assembled it all and took it for a test run. Blow me, the surge was improved but still there. Back to the shed, took off the end cover (really just a hollow plug) which sits over the end of the rack, then fired up again to see if I could feel the rack movement, just in case I was looking in the wrong area. Engine seemed better and the rack was steady so I went for another run. Problem gone!! I ran out of light and had to walk away but it seems the end of the rack is somehow sticking in the cover plug. Very strange.
Don't know what's available in your area nutwood, but might help a bit to use some form of additive in fuel that cleans and lubricates injection pump and injectors. Also, make certain there is not water/condensation in bottom of tank. I've worked on a few machines that have sat for a spell, a bit of water in system trapped in injection pump, and the water caused rust inside the pump.